1. Field of the Invention
The present invention relates to a thermal head and a method of manufacturing the same, in which an oxidation-proof layer and an abrasion resisting layer are formed on a heating resistor layer and an electric conductor layer.
2. Description of the Prior Art
Conventionally, a thermal head of the kind as described above is arranged, for example, as shown in FIG. 4. That is, a glaze layer 12 is formed on the surface of an insulating substrate 11 such as alumina, and a heating resistor layer 13 made of Ta.sub.2 N, or the like, is formed on the glaze layer 12. A power feeding conductor layer 14 of a predetermined pattern is formed on the heating resistor layer 13. An oxidation proof layer 15 made of SiO.sub.2, or the like, and an abrasion resisting layer 15 made of Ta.sub.2 O.sub.5, or the like, are formed in this order on the layer 14. Therefore, by supplying a current to the heating resistor layer 13 and the power feeding conductor layer 14, a heating portion 17 covered with only the heating resistor layer 13 produces heat so that thermal recording is performed on a recording paper 18 through an ink ribbon, or the like (not shown). In this case, the oxidation-proof layer 15 serves to prevent the heating resistor layer 13 from being oxidized and the abrasion resisting layer 16 serves to protect the thermal head from abrasion by the recording paper 18.
In the thermal head, however, an air gap lies between the heating portion 17 and the recording paper 18 and prevents heat from being transmitted, so that there occurs deterioration in printing quality and reduction in thermal efficiency.
In order to solve the problem, as shown in FIG. 5, a thermal head is proposed, in which a metal layer 19 made of such as Ni, or the like, is provided on a portion corresponding to a heating portion 17 on an oxidation proof layer 15 and covered with an abrasion resisting layer 16. In the thus arranged thermal head, the above-mentioned air gap between the heating portion 17 and the recording paper 18 in FIG. 4 arrangement is obviated and a metal layer 19 of good thermal conduction is disposed in a heating portion 17, so that the thermal conductivity as well as the printing quality are improved. That is, as shown in FIG. 6, thermal heads A.sub.1 and A.sub.2 each provided with the metal layer 19 may provide higher printing density than thermal heads B.sub.1 and B.sub.2 in which no metal layer 19 is formed. In the cases of the thermal heads A.sub.1 and B.sub.1 a driving pulse of 4 ms is used, while in the thermal heads A.sub.2 and B.sub.2 a driving pulse of 3 ms is used. Further, as shown in FIG. 7, with respect to the temperature distribution of the thermal dots, the temperature distribution of the thermal heads A.sub.1, A.sub.2 and A.sub.3 each provided with the metal layer 19 is equal and flat. In FIG. 7, the thermal dot size is 0.45 mm in the thermal head A.sub.1, 0.21 mm in A.sub.2 and B.sub.2, and 0.13 mm in A.sub.3. The thermal head B.sub.2 has no metal layer 19. These effects are caused by the fact that the thermal conductivity of the metal layer 19 is higher by two orders than the surrounding.
In such a thermal head having the metal layer 19, however, the metal layer 19 is further covered with the abrasion resisting layer 16, so that there has been a disadvantage that the manufacturing cast increases.